1. Field of the Invention
The present invention relates to a method and to a device for producing a y-fitting having a y-branch from a metal tube by hydroforming. In many fields, use is made of tubular metal parts which comprise a main portion to which a y-branch is connected. These parts are commonly used, for example, to form connections or branches in pipes in which a fluid flows.
2. Description of the Related Art
To manufacture this kind of part it is known to use a method called hydroforming which consists in placing a straight, or curved, metal tube in a cavity of a die comprising a branch corresponding to the desired shape of the y-branch that is to be produced and in gradually causing the metal to flow into this y-fitting by applying pressure to the inside of the metal tube.
For this purpose, a fluid is injected at high pressure into the tube and at the same time pistons, which can move in the die, are applied in a sealed manner to each end of the tube so as to exert thrust on these ends and force the metal to flow into the branch of the die. Then, the free end of the y-branch is cut off so as to open the tapping.
The flow of metal into the branch is controlled by a counter-plunger arranged in the branch and moving in translational movement at the same time as the metal gradually forms the y-branch under the effect of the pressure exerted on the inside of the tube. The counter-plunger is connected to an element which exerts resistance to, or a force which opposes, the flow of metal during the displacement of this counter-plunger in the branch so as to allow the metal to flow uniformly.
However, the known devices used for producing a y-fitting from a metal tube have drawbacks. Specifically, the counter-plunger can be moved in translational movement in the branch of the die between a first position located close to the region where the cylindrical portion and the branch meet and a second position away from this region and separated by a distance which corresponds to the length of the y-branch that is to be produced. Depending on the device used, the counter-plunger extends into the branch either at a right angle with respect to the axis of the branch or parallel to the axis of the cylindrical portion of the die cavity.
When the counter-plunger extends at a right angle with respect to the axis of the branch, an empty space remains, when the counter-plunger is in the first position, between the counter-plunger and that portion of the tube facing the branch. This free space prohibits or impedes the control of the metal flow at the start of the deformation of the branch, which creates a risk that the metal bursts.
When the counter-plunger extends parallel to the axis of the cylindrical portion of the die cavity, the y-branch produced by the flow of metal into the branch has an end wall which also extends parallel to the axis of the tube. The free end of the y-branch is cut off in a direction at a right angle with respect to the axis of this y-branch so that part of the y-branch is removed, thus reducing its length.